Alkmaar. Despite suffering from injuries, Van der Gun went on to make thirty–six appearances and scoring thirteen times in all competitions. Van Der Gun made his first appearance of the 2001–02 season against Roda JC, starting a match and playing 83 minutes, in a 1–1 draw. However, he suffered a knee injury while training and was sidelined for the most of the 2001–02 season. By November, Van der Gun spent the next three months, recovering slowly from his injury, as he began making his return to training. It wasn't until on 28 February 2002 when he made his return from injury, coming on as a 76th-minute substitute, in a 1–1 draw against Fortuna Sittard. However, his return was short–lived when Van Der Gun suffered ankle injury that saw him out for the rest of the 2001–02 season. At the end of the 2001–02 season, he went on to make two appearances in all competitions. Ahead of the 2002–03 season, Van Der Gun was expected to leave Ajax following a not so satisfactory from last season. He was then loaned to Willem II for the 2002–03 season. Van der Gun made his debut for the club, coming on as a 70th-minute substitute, in a 1–0 loss against Roda JC on 31 August 2002. A month later on 28 September 2002, he scored his first goal for Willem II, in a 5–2 win against FC Zwolle. This was followed up by scoring his second goal for the club, in a 1–1 draw against SC Heerenveen. On two occasions, he played twice against his parent club, Ajax, on 3 November 2002 and 2 February 2003, as the club lost both matches. Van der Gun then scored three more goals by the end of the year. He then scored his sixth goal for Willem II, in a 3–0 win against FC Zwolle. On 14 April 2003, it was announced that he would be returning to his parent club at the end of the 2002–03 season. Van Der Gun became a first team regular for the club, as he went on to make thirty appearances and scoring six times in all competitions. Ahead of the 2003–04 season, Van Der Gun said he will be fighting for his place in the first team for Ajax. However, Van Der Gun was dropped from the first team squad. On 4 September 2003, Van Der Gun signed for ADO